Does using soil always = gnats?


All my indoor grows, no matter what soil or mix I make somehow I’m always fighting a gnat issue so my question is are gnats just part of using living soil ?

I understand literally ALL the methods used to control gnats but tired of dealing with them so just trying to decide if maybe I should try hydro and avoid soil



It does seem gnats are forever in whatever dirt you get.
I grow in coco and still see a few at times.
With dirt you can let the soil dry out between watering’s and knock them down. Or a top dressing of diatomaceous earth will kill them as they emerge from the soil. Or add some BT bits to the top inch or so or even mix the BT bits in water to kill them. Need to do it every 3 to 5 days for a couple weeks to kill them all. But as for the cause I think they are just part of the ecosystem. When sellers mix up their soils there is all kinds of life in it. Unless they kill everything by cooking it then we are going to get bugs too.


They are a continuous battle. The more organic, the more gnats. I grow in FFOF or Roots Organic. Both get them, but the RO gets them ten times worse. I do a soak in a mosquiyo bit tea every week or two depending on how bad they get. I also put mosquito bits in the soil before i plant and sprinkle some on top.


I honestly dont mind them if their presence is minimal. But when i start thinking I’m seeing floaters, or when the topsoil looks like it’s moving, then it’s time to go all Orkin Man.


I’ve used alot of different types of chemicals, however, I have no idea what they are doing to the plants structure or growth so I prefer not to use harsh ones.

This top is fought my attention. Organic living soil dose not always equal gnats. If you are trying to go for the living soil I would “not” let your soil dry out like most. If you have any beneficial life in the soil and it drys out you will probably kill most of it off.
Once you get the soil food web in line with one another those problems will slowly start to disappear. The first big thing I seen in your post was saying RO has a huge gnat population. So very true! They have been know for this issue for years now.
Maybe try looking into PureCrop1 as a soil drench. I haven’t used it like this per-say but it would probably help you out. It’s truly an amazing product.
Happy farming…


I kept fighting them but once I added a Bug Zapper they went away and haven’t heard a “Zap” out them.

I’ve since went all Hydroponic DWC and haven’t had to worry about them.

I used some beneficial microbes in my soil to promote a good root zone. Then I top with an inch or two of inert barrier, washed sand, to separate the food organics from the bugs.
If you use DE, dust the top of your soil after watering. It will usually wash away after watering so it needs to be re-applied after.
Clean your buckets/bags inside tent with H2O2 and finish with some Capt. Jacks every three days.
Never bring anything from the outside into your indoor growing environment unless you can quarantine for a week.
The Bug Zapper was the final Brick in the Wall for me. Once that was in place the mature gnats had to visit and never had the problem again.

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Do you have any UV in your tent? I’d had a small horde living in one of my tents. Added UV and within a week they were almost completely gone.


Good choice! My bug zapper has a UV light and small fan.

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If you are growing in soil, and have an excessive gnat population. You are more than likely overwatering the soil.
I like to use a container large enough,(usually a 5 gallon) to go at least 3 days between waterings. I use a moisture meter and only water when the top half of the container is dry, and the bottom is starting to dry. Since they lay their eggs in the top couple inches of soil. It may take some time but the dry cycle on the top of the soil will eventually brake the gnats lava/adult cycle. I usually only see a few of them with this technique. I have bought new soil that came full of gnats, and this technique got them under control without using insecticides.

I believe I read on this forum to mix Mosquito Bits into the soil when first used / mixed etc. The bacillus thuringiensis in MB kills the larvae when the larvae consume it.
Information on bacillus thuringiensis from National Pesticide Information Center
[Bt Fact Sheet]

I thought that I was spelling larvae wrong, thanks

It is amazing how these gnats come out of nowhere. My wife keeps a very clean house. But if we leave a tomato that is going bad on the counter for a day or so, the little suckers are all over it.

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Believe me. Spelling is not one of my strong attributes.

I always mix in DE when I make up my soil for a grow and top dress once as they go into flower and have very few gnats at all. I also run my exhaust fan open inside the tents with the fan and carbon filter on top of the tents. No more gnats when they get close to the intake for the fan. Prefilter inside the carbon filter catches there remains.

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Thank goodness for spell check! Provided that you at least know the first two letters. I sometimes can’t do this.

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I may be wrong here, but I don’t think that you can filter out gnats like other insects. I believe that the fungus from the damp soil is what produces the gnat from the start. Then they lay their larvae in the soil and then the population really explodes. I guess that why it is called a fungus gnat.
These gnats can be tricky to know if you have under control. After you kill off the adults, the larvae can be in the soil for weeks waiting for enough moisture to make their comeback.
If anything I have said is incorrect, please set me straight.
Are there more than one type of gnat?

I don’t know what to tell you… They have a fast life cycle. I keep DE in my soil and don’t have issues. The adults dig into the soil to reproduce and the DE kills them if they get in. Then the DE kills the larva. I always let the top of the soil get crusty before I water. That makes it hard for the adults to dig in and the new born to break out of the soil. It’s just a game that’s played with mother nature. We had some flash flooding early on this summer. Low and behold we had a explosion of ants and gnats. We where lucky and we didn’t have a bunch of either get into the house because we went full chemical warfare on them outside. But the few of each that made it inside didn’t last long when they got to the tents. No more than two days and they were ferts for the plants.

Please don’t misunderstand, I not saying anything negative about what you are doing. I am just saying that the DE is doing most of the work in your gnat control.

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Yes DE is doing most of it in the event I get them and also supplying silica to the plant. Also letting the top of the soil crust up a tad between watering/feeding helps. Another reason I use plastic pots. It helps keep your soil in fortress and prison mode which helps on attraction and trapping. What attracts the gnats is moisture. If they find the proper environment from finding the moisture they hang around and reproduce. That’s why a lot of folks have gnat issues in seedling to early flower when humidity in the grow is at it’s higher rates. Mid to late flower humidity levels should be dropped thus less attraction.